The present invention relates generally to operations performed in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides an improved expandable well screen for use in such operations.
It is well known in the art to convey a well screen into a subterranean well in a radially reduced configuration and then, after the screen has been appropriately positioned within the well, to radially expand the screen. Such expandable screens are beneficial where it is desired to position the screen below a restriction in the well, such as a restriction due to damaged casing, variations in open hole wellbore diameter, the need to pass the screen through a relatively small diameter tubular string before placing the screen in operation in a larger diameter tubular string or open hole, etc.
Presently available expandable well screens are constructed of multiple circumferentially distributed screen segments overlying an expandable inner tubular member. An outer shroud protects the screen segments against damage as the screen is being conveyed in the well, and ensures that each segment is appropriately positioned in contact with the inner tubular member and the adjacent segment, so that each segment is supported by the inner tubular member and no fluid leakage is permitted between adjacent segments, when the screen is expanded downhole. The inner tubular member has a large number of longitudinally extending slots formed therethrough, with the slots being circumferentially and longitudinally distributed on the tubular member. When the inner tubular member is expanded, each of the slots expands laterally, thereby becoming somewhat diamond-shaped.
Unfortunately, there are several problems associated with these types of expandable well screens. For example, manufacture is quite difficult due to the requirement of attaching individual screen segments to the inner tubular member in a circumferentially overlapping manner, and the requirement of positioning the segments within the outer shroud. Construction of the outer shroud is critical, since the shroud must be expandable yet sufficiently strong to maintain each screen segment in contact with an adjacent segment when the screen is expanded. If the screen segments are not in contact with each other, fluid may flow into the screen between the segments. Additionally, the inner tubular member configuration makes it difficult to connect the screen to other tubular members, such as blank sections of tubing, other screens, etc.
From the foregoing, it can be seen that it would be quite desirable to provide an improved expandable well screen. It is accordingly an object of the present invention to provide advancements in the technology of expandable well screens.